It sounds related to concentration problems, and mercury is well knownn to mess up people's ability to focus and concentrate.

The heartbeat symptoms are typical adrenal gland symptoms. I have problems with it too. The more stressed out I get, the worse my adrenal gland symptoms get. I'm at the height of some stress now, so when I go to bed, my heartbeat shakes my whole body, and no matter how tired I am or how relaxed I feel, it keeps me awake most of the night. As Dawn said, mercury is often the root cause for adrenal and thyroid glands getting messed up. And once your adrenal is shot, it also negatively affects concentration.

I hope you get it figured out soon, and start to feel better.

~Tia